The proliferation of personal computing devices in recent years, especially mobile personal computing devices, combined with a growth in the number of widely-used communications formats (e.g., text, voice, video, image) and protocols (e.g., SMTP, IMAP/POP, SMS/MMS, XMPP, etc.) has led to increased concerns regarding the safety and security of documents and messages that are sent over networks. Users desire a system that provides for the setting of custom, e.g., user-defined, access permissions for all or part of a file, including audio files that may or may not have been encoded using compression techniques.